Peak-to-average power ratio (PAPR) of a signal refers to the ratio of peak instantaneous power to the average power, as measured over a period of time (or time window). Alternatively, the peak-to-average ratio also refers to peak amplitude of the signal envelope to the average amplitude of the signal envelope measured over a period of time. In general, peak-to-average power ratio represents the characteristic of the signal variations. For example, a signal with a high peak-to-average power ratio may contain rare/occasional peaks, spikes or overshoots. In general, a signal having high peak-to-average power ratio causes inefficiencies in processing the signal. For example, a power amplifier that amplifies a signal having a high peak-to-average ratio often works with low efficiency (e.g., consumes more power). Similarly, in case of an analog-to-digital (A/D) converter that converts a high PAPR analog signal to digital form, the entire dynamic range of the A/D converter is not efficiently utilized.
The reduction of PAPR in orthogonal frequency division multiplexing (OFDM) systems is beneficial because it improves the transmitter efficiency which is an important system parameter for conserving power in battery operated devices, for example. In one example conventional method, the PAPR of an OFDM signal can be reduced by analyzing the peaks of a given signal and reducing their absolute value. One option to achieve this goal is by clipping the base-band envelope to a certain threshold while maintaining the phase, where this operation is referred to as soft clipping. An issue with this approach is that it usually results in major degradation to other desired system parameters such OFDM signal quality which may be quantified by its error vector magnitude (EVM) and spectral mask, for example. In most communication standards and systems, there are strict requirements on the EVM and spectral mask properties of the signal and thus, the amount of PAPR reduction achievable by soft clipping alone is limited.